1. Field of the Invention
This invention relates to heat exchangers and, more particularly, to a support plate for supporting tubes in a heat exchanger.
2. Description of the Related Art
Support plates for closely packed tubes in heat exchangers are generally known. Such a support plate is shown, for example, in Japanese Patent Document JP-P-HEI 4-292797 issued to Urabe. Generally, the Urabe heat exchanger is designed for use in an air conditioning system of a motor vehicle. As such, the tubes are typically subjected to vibration from the motor vehicle and from the flow of refrigerant fluid in the cooling circuit. This vibration may cause the tubes to shift, bend, break or otherwise become damaged. Damage to the tubes may, in turn, cause the space between adjacent tubes to be non-uniform and the air flow, which passes across the tubes, to become uneven. This can result in a decrease in the heat exchange efficiency of the heat exchanger. Also, the air resistance of the heat exchanger may increase. Because of these problems, a heat exchanger may be provided with a tube support system to inhibit lateral movement of the tubes.
Referring to FIG. 1 of Urabe, a tube support plate 32 for supporting closely packed heat transfer tubes 15 is typically transversely disposed with respect to heat transfer tubes 15 in the heat exchanger. Tube support plate 32 has a plurality of holes 33, each of which receives a plurality of heat transfer tubes 15. Holes 33 are circular in shape and are respectively identical to, or slightly larger in diameter than, heat transfer tubes 15 to support heat transfer tubes 15 against lateral movement. Referring also to FIG. 2, each hole 34 includes a plurality of projection portions 34a extending from an edge thereof. Projection portions 34a contact with an outer surface of a heat transfer tube 15 so as to inhibit lateral movement of heat transfer tube 15. A relatively small gap 44 is created between the edges of holes 34 and heat transfer tubes 15.
Generally, the air flow contains moisture in a vapor state. Typically, the vapor is cooled to a temperature below the dew point as the air flow passes across the heat transfer tubes. This temperature reduction changes the vapor into a condensate, which can form on and adhere to the outer surfaces of the heat transfer tubes.
In the Urabe heat exchanger, the condensate which forms on the outer surfaces of heat transfer tubes 15, can move to and collect on tube support plate 32 if the outer surfaces of heat transfer tubes 15 contact the inner edges of holes 33 as shown in FIG. 1. This is undesirable for a variety of reasons including the propagation of rust on plate 32. To solve this problem, the diameter of holes 33 may be enlarged. However, if the diameter of holes 33 is enlarged to avoid contact with tubes 15, support for tubes 15 may become greatly reduced. Alternatively, as shown in FIG. 2, projections 34a may be provided to create a gap 44 between the outer surface of heat transfer tube 15 and the edge of hole 34 as shown FIG. 2. However, this alternative solution might present similar problems already considered. For example, if gap 44 is too small, the condensate can encounter difficulty in flowing along the surface of tube 15 and past plate 32. Thus, condensate may move to and collect on plate 32. If projections 34a are elongated to enlarge gap 44, the strength of projection 34a might become weak and projections 34a may be more easily damaged.
Other problems also exist. For example, condensate which collects on tube support plate 32 can be carried to the outside of heat exchanger 10 by the air flow. Thus, engine parts in the vicinity of such a heat exchanger used in a motor vehicle are subject to problems such as corrosion or rust. Moreover, the air resistance of heat exchanger 10 might increase since condensate on plate 32 and tubes 15 disrupts the air flow passing across tubes 15. Because of these and other problems, the heat exchanger cannot maintain the high heat exchange efficiency over extended periods of use.